System and method of speed detection in an ac induction machine

ABSTRACT

A system and method for determining rotor speed of an AC induction machine is disclosed. The system is programmed to estimate a rotor speed of the induction machine according to a linear speed estimation algorithm and based on name plate information (NPI) of the induction machine and parameters of the AC induction machine during operation thereof. The rotor speed estimation system is also programmed to estimate a rotor speed of the AC induction machine according to a frequency-domain signal processing algorithm and determine if the rotor speed estimated thereby is valid. If the rotor speed estimated by the frequency-domain signal processing algorithm is valid, then a tuned rotor speed of the AC induction machine is estimated according to the linear speed estimation algorithm and based, in part, on the rotor speed estimated by the frequency-domain signal processing algorithm.

BACKGROUND OF THE INVENTION

The present invention relates generally to AC induction machines and,more particularly, to a system and method for determining rotor speed ofan AC induction machine.

Electric motors consume a large percentage of generated electricitycapacity. Many applications for this “workhorse” of industry are fan andpump industrial applications. For example, in a typical integrated papermill, low voltage and medium voltage motors may comprise nearly 70% ofall driven electrical loads. Due to the prevalence of these motors inindustry, it is paramount that the electric motors be operated reliablyand efficiently. Motor design parameters and performance parameters areoften required by motor management systems to optimize the control andoperations of electric motors. Similarly, motor status monitoringenables the electric motors to operate reliably. Many motor statusmonitoring techniques also look for certain motor design parameters andperformance parameters.

One such motor performance parameter that is helpful in optimizing thecontrol and operations of electric motors is rotor or motor speed. Thereare many different techniques for estimating motor speed, includingcomplex techniques that are highly accurate but unreliable (i.e., notuseful under all conditions) and simplistic techniques that are morereliable but less accurate. Two such motor speed estimation methods,respectively, are (1) motor equivalent models or complex digital signalprocessing techniques, such as Fast Fourier Transform (FFT) or otherfrequency-domain signal processing operations, or (2) a technique thatimplements a linear speed-load curve derived from rated motor speed(RPM) and synchronous speed (RPM). However, each of these techniques haslimitations regarding the availability of implemented and/or limitationsregarding the accuracy of the motor speed estimation.

With respect to implementing of FFT based speed estimation techniques,it is recognized that for low-end motor control or monitoring products,these techniques often may not be implemented because of hardware andsoftware restrictions. Additionally, it is recognized that suchtechniques may not be reliable. That is, the accuracy is relatively highwhen a signal contains enough speed related information; however, whensuch information is not sufficient, the method can give inaccurateresults.

With respect to linear speed estimation techniques, it is recognizedthat implementation may be limited to motors operating under ratedconditions (rated voltage and rated frequency). However, for motors thatare operating under rated conditions, such as inverter-fed motors, suchmotor speed estimation often cannot be used since the rated RPM in thenameplate is only valid for rated motor operations (e.g., at a ratedvoltage and a rated frequency). Additionally, even for linear speedestimation techniques that can be implemented with inverter-fed motors,it is recognized that errors in the linear motor speed may be presentdue to error in the rated speed from the name plate information of themotor and non-linear load-speed characteristics of the motor. While sucherrors may be small (less than 4%), it is still desirable to compensatefor such errors in order to derive a more accurate motor speedestimation.

It would therefore be desirable to design a system and method fordetermining speed of an AC induction machine that is not dependent onset load, voltage, and frequency conditions, so as to enable theimproved management and status monitoring. It would further be desirablefor such a system and method to provide accurate estimation of the speedin a reliable fashion, regardless of the exact operating conditions ofthe AC induction machine.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide a system and method fordetermining rotor speed of an AC induction machine.

In accordance with one aspect of the invention, a rotor speed estimationsystem is programmed to estimate a rotor speed of an AC inductionmachine according to a linear speed estimation algorithm and based onname plate information (NPI) of the AC induction machine and parametersof the AC induction machine during operation thereof, with theparameters comprising voltage and frequency values of power input to theAC induction machine and a load value of the AC induction machine. Therotor speed estimation system is also programmed to estimate a rotorspeed of the AC induction machine according to a frequency-domain signalprocessing algorithm and determine if the rotor speed estimated by thefrequency-domain signal processing algorithm is valid. If the rotorspeed estimated by the frequency-domain signal processing algorithm isvalid then the rotor speed estimation system estimates a tuned rotorspeed of the AC induction machine according to the linear speedestimation algorithm and based, in part, on the rotor speed estimated bythe frequency-domain signal processing algorithm and stores the tunedrotor speed on a computer readable storage medium.

In accordance with another aspect of the invention, a method ofdetermining rotor speed of an AC induction machine includes accessingname plate information (NPI) of an AC induction machine, with the NPIincluding a rated power, a rated speed, a rated frequency, and a ratedvoltage of the AC induction machine. The method also includesdetermining each of a voltage value and a frequency value of power inputto the AC induction machine during operation thereof, determining a loadpercentage from the AC induction machine during operation thereof, andestimating a rotor speed of the AC induction machine in operation basedon the NPI, the voltage and frequency values of the AC inductionmachine, and the load percentage of the AC induction machine. The methodfurther includes calculating a revised rated speed of the AC inductionmachine, estimating a tuned rotor speed of the AC induction machinebased on the NPI, the voltage and frequency values of the AC inductionmachine, and the load percentage of the AC induction machine, with therevised rated speed replacing the rated speed from the NPI forestimation of the tuned rotor speed, and storing the tuned rotor speedon a computer readable storage medium.

In accordance with yet another aspect of the invention, a non-transitorycomputer readable storage medium has stored thereon a computer programcomprising instructions which, when executed by at least one processor,cause the at least one processor to acquire a first estimate of a motorspeed of an AC motor according to a linear speed estimation algorithmand based on name plate information (NPI) of the AC motor and parametersof the AC motor during operation thereof. The instructions also causethe at least one processor to acquire a second estimate of the motorspeed of the AC motor according to a frequency-domain based speedestimation algorithm, perform a validation process on the secondestimate of the motor speed of the AC motor, and calculate a rated speedvalue for the AC motor based on the validated second estimate of themotor speed of the AC motor. The instructions further cause the at leastone processor to input the calculated rated speed value into the linearspeed estimation algorithm to acquire a tuned estimate of the motorspeed of the AC motor and store the tuned motor speed on the computerreadable storage medium.

Various other features and advantages of the present invention will bemade apparent from the following detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate preferred embodiments presently contemplated forcarrying out the invention.

In the drawings:

FIG. 1 is schematic of a control system including a motor drive systemaccording to one aspect of the invention.

FIG. 2 is a schematic of a control system including a motor drive systemaccording to another aspect of the invention.

FIG. 3 is a schematic of a control system including a motor drive systemaccording to yet another aspect of the invention.

FIG. 4 is a schematic of a control system including a motor protectionsystem according to one aspect of the invention.

FIG. 5 is a schematic of a control system including a motor startersystem according to one aspect of the invention.

FIG. 6 is a technique for determining rotor speed of an electric motoraccording to an embodiment of the invention.

FIG. 7 is a graphical representation of load-speed curves of a motoroperating at a selected voltage-frequency and at a ratedvoltage-frequency.

DETAILED DESCRIPTION OF THE INVENTION

Several embodiments of the invention are set forth that relate to asystem and method of estimating speed of an AC induction machine, whichmay be fed by a fixed frequency supply or a variable frequency supply.Embodiments of the invention thus encompass various types of ACinduction machines, including both motors and generators, both singlephase and multi-phase, and all voltage levels (low-voltage, mediumvoltage, and high voltage). The system selectively implements a linearspeed estimation algorithm and a frequency domain based speed detectionalgorithm to determine speed of the AC induction machine.

Various speed estimation systems are shown and described in FIGS. 1-5with respect to AC motors, according to embodiments of the invention.Referring now to FIG. 1, a general structure of a motor assembly 10 isshown. Motor assembly 10 includes a motor drive 14, which may beconfigured, for example, as an adjustable or variable speed drivedesigned to receive a three-phase AC power input power input 16 a-16 c.Alternatively, motor assembly 10 may be configured to drive amulti-phase motor. According to one embodiment of motor assembly 10, adrive control unit 18 is integrated within motor drive 14 and functionsas part of the internal logic of the drive 14, although it is recognizedthat embodiments of motor assembly 10 may not include such a drivecontrol unit.

Motor drive 14 also includes a drive power block unit 20, which may, forexample, contain an uncontrollable or controllable rectification unit(uncontrolled AC to DC), a filtering inductor, a DC bus capacitor orbattery, and a pulse width modulation (PWM) inverter (DC to controlledAC). Alternatively, drive power block unit 20 may be provided withoutsuch a rectification unit such that the DC bus is directly connected tothe inverter. A drive power block unit may be provided without arectification unit when applied to an uninterruptible power supply(UPS), for example.

Drive 14 receives the three-phase AC input 16 a-16 c, which is fed todrive power block unit 20. The drive power block unit 20 converts the ACpower input to a DC power, inverts and conditions the DC power to acontrolled AC power for transmission to an AC motor 22.

Motor assembly 10 also includes a drive user interface 24 or drivecontrol panel, configured to enable users to input motor parameters anddrive operating parameters and other parameters necessary for the driveoperation. User interface 24 is also used to display a list of motoroperating parameters, such as, for example, motor input voltage (rms),motor current (rms), motor input power, speed, torque, etc., to the userfor monitoring purposes.

Motor assembly 10 includes a speed detection algorithm module 26 thatreceives voltage and current signals 28 input to motor 22. According toone embodiment, speed detection algorithm module 26 is integrated withindrive 14 and functions as part of the internal logic of drive 14.Alternatively, speed detection algorithm module 26 may be embodied in anexternal module distinct from drive 14, and receive data therefrom(e.g., current and/or voltage signals), as described in more detail withrespect to FIGS. 2 and 3.

Referring now to FIG. 2, a motor assembly 30 is shown according to anembodiment of the invention. Motor assembly 30 includes a variablefrequency motor drive 32 and a drive user interface 34. Also included inmotor assembly 30, external to drive 32, is a standalone externalhardware unit identified as a speed detection algorithm module 36. Speeddetection algorithm module 36 receives voltage and current signals,including single-phase current and voltage signals, multiple-phasecurrent and voltage signals, or combinations thereof, which may be usedto determine operating conditions. A user interface 38 is coupled tostandalone external speed detection algorithm module 36. A drive controlunit 40 and drive power block unit 42 are included within motor drive32.

Speed detection algorithm module 36 is a separate hardware moduleexternal to the existing hardware of motor drive 32 and may be installedin an existing motor drive and exchange data through existing drivecommunications, such as, for example, ModBus, Device Net, Ethernet, andthe like. Module 36 uses a set of voltage sensors 44 to measure themulti-phase line-to-line voltages of a motor 46. Module 36 also includesa set of current sensors 48 to measure the multi-phase currents of motor46. For a three phase current, for example, where no neutral point isavailable, module 36 includes at least two current sensors for athree-wire system. As the three phase currents add to zero, the thirdcurrent may be calculated from the other two current values. However,while a third sensor is optional, such sensor increases the accuracy ofthe overall current calculation.

FIG. 3 illustrates a motor assembly 50 including an external speeddetection algorithm module 52 in accordance with another embodiment ofthe present invention. Similar to the motor assembly described withrespect to FIG. 2, motor assembly 50 includes a drive user interface 54and a variable frequency drive 56 having a drive control unit 58 and adrive power block unit 60. However, unlike the motor assembly of FIG. 2,external module 52 does not have its own voltage and current sensors.Instead, external module 52 is implemented in a computing device thatobtains voltage and current signals 62 via a data acquisition unit 64.

Referring now to FIG. 4, a motor protection system 66 is illustrated inaccordance with yet another embodiment. System 66 includes a motorprotection assembly 68 having at least one motor protection device 70such as, for example, a contactor assembly having a number ofindependently controllable contactors configured to selectively controlthe supply of power from an AC power source 72 to a motor 74. Motorprotection assembly 68 also includes a speed detection algorithm module78 that receives voltage and current data from sensors 80. Speeddetection algorithm module 78 analyzes the voltage and current data,along with additional data, to determine the speed of the motor 74 andtransmits a signal indicative of the speed to a communication module 82.While speed detection algorithm module 78 is shown as being incorporatedinto assembly 68, it is recognized that speed detection algorithm module78 could also be implemented as an external module with its own sensors(e.g., module 36 in FIG. 2) or as an external module without sensors(e.g., module 52 in FIG. 3).

According to another embodiment of the present invention, a motorstarter system 84 is illustrated in FIG. 5. Motor starter system 84includes a soft starter 86 having a number of semi-conductor devices 88,such as thyristors and/or diodes, to transmit a supply power between apower source 90 and a motor 92. A speed detection module 94, similar tospeed detection algorithm module 26 of FIG. 1, is included within softstarter 86 and is configured to interface with communication module 96.While speed detection algorithm module 94 is shown as being incorporatedinto soft starter 86, it is recognized that speed detection algorithmmodule 94 could also be implemented as an external module with its ownsensors (e.g., module 36 in FIG. 2) or as an external module withoutsensors (e.g., module 52 in FIG. 3).

Referring now to FIG. 6, a technique 100 for determining rotor speed ofan AC induction machine in operation is shown that can be implemented,for example, in any of the systems shown in FIGS. 1-5. While technique100 is discussed below with respect to determining rotor speed in an ACmotor, it is recognized that technique 100 may also be used to determinerotor speed from a variety of AC induction machines (e.g., generators),both single phase and multi-phase, and at any voltage level. Thus, withrespect to the embodiment shown and described in FIG. 6, technique 100may be used to determine the motor speed of single-phase motors,multi-phase motors, inverter driven motors such as variable frequencydriven motors, AC motors coupled to a soft-starter, and other types ofAC motors or AC motor configurations. Further, embodiments of theinvention are not limited to motors operating only at a rated frequencyor voltage of the motors. Rather, embodiments of the invention, such astechnique 100, are effective at estimating motor speed of AC motors thatoperate with varying input voltage(s) and/or varying inputfrequency(ies).

Technique 100 provides a method of speed detection that is capable ofusing both a linear speed estimation algorithm and a frequency-domainanalysis based speed detection algorithm to determine motor speed of theAC motor. According to an exemplary embodiment of the invention, an FFTspeed detection algorithm can be implemented as the frequency-domainbased processing method, with the speed estimated by the FFT speeddetection algorithm being used to “tune” the speed estimated by thelinear speed estimation algorithm. Technique 100 begins at block 102,where motor nameplate data or motor nameplate information (NPI) isaccessed. According to embodiments of the invention, the NPI includesthe rated operating frequency of the motor, the rated operating voltageof the motor, the rated operating speed of the motor, and the ratedoperating output power of the motor. These NPI parameters are availablefor electric motors on their nameplate tag. Such NPI may be accessedfrom a variety of sources. For example, NPI may be manually input by auser through a user interface. In addition, NPI may be accessed from amemory unit located either internal or external to a motor drive, whichcontrols the motor. It is also envisioned that NPI could be gathered oraccessed from a network such as, for example, the Internet.

After motor NPI is accessed/read, motor input voltage and current areread at block 104, such as by way of a plurality of voltage and currentsensors. Upon reading of the motor input voltage and current, thetechnique continues at block 106, where a root mean square (rms)voltage, supply frequency, and load value (such as a load percentage orpower output of the motor during operation) are determined. Fordetermining the voltage rms, the measured voltage over time can beanalyzed to determine the voltage rms in a known manner. Fordetermination of motor voltage rms in a three-phase motor, motor inputvoltages of multiple phases may be determined and then averaged toproduce a single input voltage value, e.g., the voltage rms.

In determining motor input frequency (i.e., supply frequency) of the ACmotor at block 106, the sensed/measured motor current and voltagewaveforms and a detected the zero crossing point of the current andvoltage may be analyzed. As would be understood by those skilled in theart, it is contemplated that the input frequency may be determined fromeither the voltage or current input or induced into the motor.

Regarding calculation of the load value at block 106, the load valuemay, for example, be sensed using a sensing device such as a powermeter. Alternatively, a load value such as motor power output may beapproximated to be equal to the input power of the motor or determinedin another manner. Further details regarding the determination of theload value will be set forth in greater detail below.

It is noted that, according to embodiments of the invention, the orderin which motor input voltage, motor input frequency, motor power output,and motor NPI are determined or accessed as shown in blocks 102-106 neednot be the same as that shown in FIG. 6. Rather, NPI may be accessed andmotor input voltage, motor input frequency, and the load value may bedetermined simultaneously or in another order different than the ordershown in FIG. 6.

Referring back to the embodiment of technique 100 shown in FIG. 6, afterdetermining the voltage rms, supply frequency, and load percentage atblock 106, the technique proceeds to block 108, where the speed of themotor is determined by implementing a linear speed estimation algorithmthat determines motor speed based on the determined motor input voltage,the determined motor input frequency, the determined load value, and theaccessed NPI.

According to one embodiment of the invention, the motor speed isestimated by the linear speed algorithm according to the followingrelationship:

$\begin{matrix}{{\omega_{r\_ x} = {{\frac{\omega_{{r\_ {rated}}\_ 2} - \omega_{{{syn}\_}2}}{P_{{m\_ {rated}}\_ 2}}.P_{m\_ x}} + \omega_{{{syn}\_}2}}},} & {\left( {{Eqn}.\mspace{14mu} 1} \right),}\end{matrix}$

where ω_(r) _(—) _(x) refers to the motor speed (i.e., mechanicalangular speed of the rotor). As will be shown in detail below, thevariables of Eqn. 1 may be determined from a motor input voltage, amotor input frequency, a motor load value, P_(m) _(—) _(x), such as loadpercentage and NPI of the motor.

To estimate the speed of a motor according to the embodiment encompassedby Eqn. 1, begin by setting the accessed NPI of the motor to thefollowing:

Rated Voltage, υ_(s) _(—) ₁;

Rated Frequency, f_(s) _(—) ₁;

Rated Output Power, P_(m) _(—) _(rated) _(—) ₁; and

Rated Speed in radians per second, ω_(r) _(—) _(Rated) _(—) ₁.

These NPI parameters represent rated values at a rated motor operatingcondition (i.e., a motor operating at rated voltage and ratedfrequency).

From the NPI, a rated torque of the motor may be defined as follows:

$\begin{matrix}{{T_{{{rated}\_}1} = \frac{P_{{m\_ {rated}}\_ 1}}{\omega_{{r\_ {rated}}\_ 1}}},} & {\left( {{Eqn}.\mspace{14mu} 2} \right).}\end{matrix}$

In addition, a rated synchronous speed, ω_(syn) _(—) ₁, of the motor maybe determined in the following manner:

$\begin{matrix}{{\omega_{{{syn}\_}1} = {\frac{120 \cdot f_{{s\_}1}}{p} \cdot \frac{2\pi}{60}}},} & {\left( {{Eqn}.\mspace{14mu} 3} \right),}\end{matrix}$

where p refers to the number of poles of the motor.

Next, a rated slip, s_(rated) _(—) ₁, of the motor may be determined inthe following manner:

$\begin{matrix}{{s_{{{rated}\_}1} = \frac{\omega_{{{syn}\_}1} - \omega_{{r\_ {Rated}}\_ 1}}{\omega_{{{syn}\_}1}}},} & {\left( {{Eqn}.\mspace{14mu} 4} \right).}\end{matrix}$

Using Eqns. 1-4 above, a speed curve representative of an AC motoroperating at rated operating parameters (e.g., rated voltage, υ_(s) _(—)₁, and rated frequency, f_(s) _(—) ₁) may be determined.

Still referring to the present embodiment, a motor speed of an AC motoroperating at any arbitrary input voltage, υ_(s) _(—) ₂, arbitrary inputfrequency, f_(s) _(—) ₂, and arbitrary load value, P_(m) _(—) _(x), cannow be determined using the following set of equations:

$\begin{matrix}{{s_{{{rated}\_}2} = {s_{{{rated}\_}1} \cdot \left( \frac{f_{{s\_}1}}{f_{{s\_}2}} \right)}},} & {\left( {{Eqn}.\mspace{14mu} 5} \right);} \\{{\omega_{{{syn}\_}2} = {\omega_{{{syn}\_}1} \cdot \left( \frac{f_{{s\_}2}}{f_{{s\_}1}} \right)}},} & {\left( {{Eqn}.\mspace{14mu} 6} \right);} \\{{\omega_{{r\_ {rated}}\_ 2} = {\omega_{{{syn}\_}2} \cdot \left( {1 - s_{{{rated}\_}2}} \right)}},} & {\left( {{Eqn}.\mspace{14mu} 7} \right);} \\{{T_{{{rated}\_}2} = {T_{{{rated}\_}1} \cdot \left( \frac{\upsilon_{{s\_}2}}{\upsilon_{{s\_}1}} \right)^{2} \cdot \left( \frac{f_{{s\_}1}}{f_{{s\_}2}} \right)^{2}}},{and}} & {\left( {{Eqn}.\mspace{14mu} 8} \right);} \\{{P_{{m\_ {rated}}\_ 2} = {T_{{{rated}\_}2} \cdot \omega_{{r\_ {rated}}\_ 2}}},} & {\left( {{Eqn}.\mspace{14mu} 9} \right).}\end{matrix}$

By implementing Eqns. 2-9, the speed, ω_(r) _(—) _(x), of an AC motoroperating at any given load (e.g., when the motor delivers any givenmechanical output power P_(m) _(—) _(x)), any given input voltage, υ_(s)_(—) ₂, and any given input frequency, f_(s) _(—) ₂, may be estimated inthe manner set forth by Eqn. 1, shown again below:

$\begin{matrix}{{\omega_{r\_ x} = {{\frac{\omega_{{r\_ {rated}}\_ 2} - \omega_{{{syn}\_}2}}{P_{{m\_ {rated}}\_ 2}} \cdot P_{m\_ x}} + \omega_{{{syn}\_}2}}},} & {\left( {{Eqn}.\mspace{14mu} 1} \right).}\end{matrix}$

In other words, as shown with Eqns. 1-9 above and the accompanyingdescription, the motor speed, ω_(r) _(—) _(x), may be estimated merelywith the determined motor input voltage, υ_(s) _(—) ₂, the determinedmotor input frequency, f_(s) _(—) ₂, the determined load value, P_(m)_(—) _(x), such as motor power output, and the accessed NPI (i.e., ratedmotor power, P_(m) _(—) _(rated) _(—) ₁, rated motor speed, ω_(r) _(—)_(Rated) _(—) ₁, rated voltage, υ_(s) _(—) ₁, and rated frequency, f_(s)_(—) ₁, of the motor). Thus, the linear speed algorithm produceseffective speed estimations at any arbitrary input voltage, υ_(s) _(—)₂, and any arbitrary input frequency, f_(s) _(—) ₂—not just at a ratedvoltage and rated frequency of the AC motor.

According to an embodiment of the invention, upon determination of themotor speed at block 108 via the linear speed algorithm using theparameters set forth above, technique continues at block 110 bycharacterizing operation of the motor as falling within a pre-determined“bin” based on the load percentage (determined at block 106). The loadpercentage is characterized to fall within, or outside of, one ofseveral bins so as to allow for compensation of the non-linearcharacteristics of a load-speed curve of the motor in a more accuratefashion. That is, as will be explained in detail below, a distincttuning of the motor speed estimated by the linear speed detectionalgorithm is desired for each bin, so as to allow for compensation ofthe non-linear characteristics of a load-speed curve of the motor. Theload bins can be defined, for example, as in the below table:

Load Bins Load Range (as % of rated load) Bin 1 40% <= load % <= 50% Bin2 50% < load % <= 70% Bin 3 70% < load % <= 90%Tuning of the motor speed estimated by the linear speed detectionalgorithm is determined to be desirable when the load percentage isdetermined to be between 40% and 90% of the rated load. According toembodiment of the invention, it may desirable to provide no additionaltuning to the motor speed estimated by the linear speed detectionalgorithm if the load percentage falls outside of the pre-determinedbins (e.g., <40% or >90% of the rated load.

Upon classification of the load percentage within or outside of certainpre-determined bins at block 110, a determination is made at block 112as to whether further “tuning” of the estimated motor speed can beperformed at that time. More specifically, a determination is maderegarding whether an estimate of a “reference” rotor bar number(R_(estimate)) for the motor has been acquired from a previous iterationof the technique 100. A flag for acquisition of the rotor bar number(R_ready_flag) can be set initially at zero (0) and be changed to one(1) upon acquisition of the rotor bar number, with it being determinedat block 112 if the flag, R_ready_flag, is currently at zero or one. Ina first iteration of technique 100, an estimate of the rotor bar numberfor the motor will not be available, and thus the flag will be at zero.When it is determined that an estimate of the rotor bar number,R_(estimate), for the motor has not yet been acquired, indicated at 114,the technique 100 will continue at block 116, where a rotor bar numberestimation routine (blocks 116-130) is initiated.

The rotor bar number estimation routine of blocks 116-130 implements afrequency-domain analysis speed detection algorithm (e.g., an FFT speeddetection algorithm) for determining rotor speed of the motor and therotor bar number of the motor. For purposes of the rotor bar numberestimation routine 116-130, the FFT speed detection algorithm is appliedfor the purpose of estimating a “reference” rotor bar number,R_(estimate), which will then be subsequently used for verification ofthe accuracy of future rotor speed estimations using the FFT speeddetection algorithm, as will be explained in detail below.

The rotor bar number estimation routine begins at block 116 withdetection of slot harmonics from the motor current frequency spectrum,as it is recognized that slot harmonics detected from the motor currentfrequency spectrum are associated with the rotor bar number of themotor. Thus, accurate slot harmonics detection is desired for providingan accurate estimate of the rotor bar number. For determining the slotharmonics, the FFT speed detection algorithm is implemented at block116. The FFT speed detection algorithm makes use of sampled statorcurrent data (acquired at block 104) for determination of a saliencyslot harmonic frequency. The slot harmonics provide desirable bandwidthspeed information and serve as the primary basis for the FFT speeddetection algorithm. According to an embodiment of the invention, thesaliency harmonic equation is provided as:

$\begin{matrix}{{f_{seh} = {f_{1}\left\lbrack {{\left( {{kR} + n_{d}} \right)\frac{\left( {1 - s} \right)}{P}} + n_{w}} \right\rbrack}},} & \left( {{Eqn}.\mspace{14mu} 10} \right)\end{matrix}$

where f₁ is the fundamental stator frequency, k is a constant, R is therotor bar number, P is the number of pole-pairs in the motor, n_(d) isan order of eccentricity, n_(w) is the time harmonic order arising fromodd phase belt harmonics of f₁, and s is motor slip.

Before the FFT speed detection algorithm can operate to identify slotharmonics, all of the machine structural parameters in Eqn. 10 need tobe determined. For Eqn. 10, it is assumed that k=1 for determination ofslot harmonics and that P can be easily determined from the nameplatefor user input. In general, the parameters s, R, n_(d) and n_(w) in Eqn.1 are unknown.

For determining the slip s, linear slip is fed as the initial slipestimate, such that the detection of slot harmonics even at low supplyfrequency (e.g., <30 Hz) is improved. Linear slip is defined by thebelow equation:

$\begin{matrix}{{{{Linear}\mspace{14mu} {slip}} = \frac{{{synchronous}\mspace{14mu} {speed}} - {{linear}\mspace{14mu} {speed}}}{{synchronous}\mspace{14mu} {speed}}},} & \left( {{Eqn}.\mspace{14mu} 11} \right)\end{matrix}$

where the synchronous speed is a known quantity (e.g., based on thenumber of poles in the motor, etc.) and the linear speed is known fromblock 108.

Having determined the slip, values are assumed for n_(d) and n_(w) inorder that the value for R can then be determined. That is, it isassumed that n_(d) corresponding to a detected slot harmonic is set tozero and that n_(w) is set to each of a plurality of odd integersettings. In setting n_(w) to each of a plurality of odd integersettings, it is recognized that each of the magnitude of the slotharmonics and the spacing between pairs of slot harmonics is used as acriterion for detecting the primary slot harmonic. The odd integersettings of n_(w) correspond to spacing between the pair of slotharmonics of approximately twice of the fundamental frequency (i.e.,spacing=2*f₁). The value for R can then be determined, with possiblevalues of R being determined given knowledge of the motor frame size andthe number of poles, and using a simple rules-based selection. Anexemplary range of rotor bar numbers for respective numbers of poles ina motor is defined in TABLE I.

TABLE I No. of poles Bar Range 2 R = [18, 20, 22, 24, 25, 26, 28, 30,32, 34, 38, 40, 44, 46, 48, 52, 60] 4 R = [22, 26, 28, 32, 36, 38, 40,44, 45, 46, 47, 48, 50, 54, 56, 58, 60, 72, 76] 6 R = [16, 26, 27, 33,36, 40, 42, 44, 45, 46, 48, 54, 55, 56, 57, 58, 60, 66, 84, 88] >=8 R =[40, 42, 44, 45, 48, 52, 58, 60, 64, 70, 80, 82, 88, 89, 92]

For each potential value of R, both n_(w)=1 and n_(w)=−1 are firstconsidered and, as set forth above, an assumption is made that n_(d)=0.Using the slip value determined from Eqn. 11, the magnitude of theinterpolated FFT spectrum can be evaluated at the precise slot harmonicfrequencies defined by Eqn. 10 for each combination of R and n_(w). Theparameter combination which matches a clear peak is assumed to indicatethe primary harmonic, with the primary harmonic having the desired valueof R associated therewith.

In addition to detection of the primary slot harmonic, and to improveslot harmonic detection under conditions where stray harmonics dominatethe primary slot harmonic in magnitude, the secondary slot harmonic isalso detected. That is, the slot harmonic second in magnitude to theprimary slot harmonic is detected and identified as the secondary slotharmonic.

Upon detecting both primary and secondary slot harmonics, one of theharmonics is chosen at block 118 as the dominant slot harmonic betweenthe primary and secondary slot harmonics for determination of theestimated rotor bar number for that iteration, R_(1 . . . N). Accordingto one embodiment of the invention, selection of one of the primary andsecondary slot harmonics is based on a rotor bar number look-up table.An example of such a rotor bar number look-up table is provided below:

TABLE II No. of poles Stator/Rotor Slot Number 2 36/28 48/38 54/46 60/524 48/40 48/56 60/44 60/76 72/58 6 54/42 54/66 72/88 72/54 72/84 8 54/7072/58 72/88 10 72/88 72/92 12 72/92

The bar number, out of the two that correspond to the primary andsecondary slot harmonics, that belongs to the set of numbers in TABLE IIfor the given pole number, is selected as the rotor bar number of themotor for that iteration, R_(1 . . . N). For example, for the given polenumber equal to 8, the rotor bar number corresponding to the primaryslot harmonic is 60 and the rotor bar number corresponding to that ofsecondary slot harmonic is 58. Comparing the two bar numbers 60, 58 tothe set {70, 58, 88} in TABLE II Error! Reference source not found, thesecondary slot harmonic is selected as the correct slot harmonic as 58belongs to the set of rotor slot numbers in TABLE II. In a case whereboth the numbers belong to the set in TABLE II, the bar numbercorresponding to the primary slot harmonic is selected as the rotor barnumber of the motor for that iteration R_(1 . . . N).

Upon selection of the rotor bar number associated with the dominant slotharmonic, R_(1 . . . N), technique continues with a determination atblock 120 as to whether an appropriate number of rotor bar numberestimates (R_count) have been collected to provide for an accurateoverall/final estimation of the rotor bar number. That is, the rotor barnumber is determined by using initial N number of rotor bar estimates. Ncould be chosen as 100 or 200 iterations basing on the algorithmexecution time. If it is determined that N number of rotor bar estimateshave not been collected (R_count<N), indicated at 124, then thetechnique continues at block 126 by outputting the previous linearlyestimated determined motor speed as the determined motor speed, beforelooping back to block 104. Blocks 116-130 of the rotor bar numberestimation routine are then repeated (upon determining at block 112 thatR_ready_flag is still at zero) to acquire another rotor bar estimate.This loop is repeated until N number of rotor bar estimates iscollected.

When N number of rotor bar estimates is collected, it is determined atblock 122 that N number of rotor bar estimates have been collected(R_count>=N), indicated at 128. The technique thus continues at block130, where a rotor bar number, R_(estimate), is selected from the Nnumber of rotor bar estimates, R_(1 . . . N). After N number ofiterations, the bar number that repeats the maximum number of times isconsidered as the estimated rotor bar number of the motor, R_(estimate).That is, R_(estimate) is equal to the bar number that repeats a maximumnumber of times in N iterations. According to one embodiment of theinvention, in order to select a rotor bar number, it is desired that theestimated rotor bar number, R_(estimate), should account for at least40% of the total number of N values. Also at block 130, upondetermination of R_(estimate), the flag for acquisition of the rotor barnumber (R_ready_flag) is set to one (1).

Upon determination of R_(estimate), the technique then proceeds fromblock 130 to block 126, where the previous linearly estimated motorspeed is output as the determined motor speed, before looping back toblock 104. Upon performing of blocks 104-110, the technique returns toblock 112, where the determination is made that “tuning” of theestimated motor speed can be performed at that time, indicated at 132,as R_ready_flag is set to one. The technique thus continues to block134, where a determination is made as to whether further “tuning” of theestimated motor speed can be performed at that time. More specifically,a determination is made regarding whether an estimate of a “new” ratedspeed for the motor has been acquired (i.e., other than the rated speedfrom the motor NPI) from a previous iteration of the technique 100. Aflag for acquisition of the rated speed (tune_flag) can be set initiallyat zero (0) and be changed to one (1) upon acquisition of the ratedspeed, with it being determined at block 134 if the flag is currently atzero or one. In a first iteration of technique 100 after havingdetermined the rotor bar number, R_(estimate), an estimate of the ratedspeed for the motor will not be available, and thus the flag will be atzero.

According to one embodiment, a tune_flag is provided for each of theplurality of bins that correspond to a load percentage of the motor.That is, as set forth above for block 110, operation of the motor isanalyzed to determine the present load percentage at which the motor iscurrently operating, with the load percentage being characterized tofall within, or outside of, one of several bins. If the present loadpercentage of the motor falls within one of the above bins, such aswithin Bin 1, it is determined at block 134 whether an estimate of therated speed for the motor has been acquired for that bin (i.e., for Bin1)

If a determination is made that an estimate of the rated speed for themotor is not available and has not been acquired for that bin (e.g., thetune_flag for Bin 1 is zero), identified at 136, technique 100 proceedsto block 138, where the slot speed of the motor is calculated using aFFT speed detection algorithm, such as by implementing Eqn. 10 set forthabove. Along with the calculation of the slot speed of the motor,application of the FFT speed detection algorithm of Eqn. 10 at block 138will also output an estimated rotor bar number, R, for the motorassociated with the slot speed.

At block 140, a determination is then made as to whether the rotor barnumber estimated at block 138, R, is equal to the rotor bar numberestimate, R_(estimate), output at block 130 from the rotor bar numberestimation routine (blocks 116-130). The determination at block 140serves to validate the slot harmonics and the corresponding calculatedslot speed in the FFT speed detection algorithm implemented at block 138for its correctness, so as to determine whether the slot speed of themotor output from the FFT speed detection algorithm is accurate forpurposes of tuning the linear speed estimated at block 108.

If it determined at block 140 that the rotor bar number estimated atblock 138 is not equal to the rotor bar number estimate, R_(estimate),output at block 130, indicated at 142, then it is determined that theslot speed calculated at block 138 from the FFT speed detectionalgorithm is not accurate. The technique 100 thus determines that theslot speed will not be implemented to “tune” the motor speed determinedat block 108 by the linear speed estimation and thus continues to block126, where the linearly estimated motor speed is output as thedetermined motor speed, before technique loops back to block 104.

Alternatively, if it determined at block 140 that the rotor bar numberestimated at block 138 is equal to the rotor bar number estimate,R_(estimate), output at block 130, indicated at 144, then it isdetermined that the slot speed calculated from the FFT speed detectionalgorithm is accurate. The technique 100 thus determines that the slotspeed should be implemented to “tune” the motor speed determined atblock 108 by the linear speed estimation and thus continues to block146, where the slot speed calculated from the FFT speed detectionalgorithm is utilized to calculate a new rated speed of the motor(Calc_NR).

Calculation of the new rated speed of the motor is illustrated in FIG.7. The slot speed calculated at block 138 (indicated at 160) is used tocalculate speed at 100% load under the same voltage and frequency inputas of the slot speed (indicated at 162). The estimated rated speed isgiven by the equation:

$\begin{matrix}{{{Estimated}\mspace{14mu} {Rated}\mspace{14mu} {Speed}} = {{\frac{\left( {{{slot}\mspace{14mu} {speed}} - {{synchronous}\mspace{14mu} {speed}}} \right)}{{load}\mspace{14mu} {percentage}}*100} + {{synchronous}\mspace{14mu} {speed}\mspace{14mu} {at}\mspace{14mu} 100\% \mspace{14mu} {{load}.}}}} & \left( {{Eqn}.\mspace{14mu} 12} \right)\end{matrix}$

The speed at 100% load at arbitrary voltage and frequency is used torecalculate the rated speed at rated voltage, frequency, and load(indicated at 164). The rated speed 164 is assumed to be a more accuratethan the rated speed provided on the motor NPI, and thus provides a moreaccurate estimation of the motor speed when implemented in the linearspeed estimation algorithm of Eqn. 1.

Referring again to FIG. 6, the new rated speed of the motor at ratedvoltage, frequency, and load, is thus calculated at block 146 via theuse of the calculated slot speed and Eqn. 12. Also at block 146, uponcalculation of the new rated speed of the motor, tune_flag is set to onefor that bin for which blocks 138-146 of technique 100 were performed.Upon calculation of the new rated speed and setting of tune_flag,technique 100 continues at block 148, where the new rated speed of themotor is used to recalculate the motor speed using the linear speedestimation algorithm, with the recalculated speed being termed the“tuned linear speed.” The new rated speed of the motor is input intoEqn. 1, where thereby the linear speed estimation algorithm outputs thetuned linear speed at block 150.

Upon estimation of the tuned linear speed of the motor, technique loopsback to block 104, for further monitoring of the motor speed. Upon againreaching block 134, a determination is again made regarding whether anestimate of the new rated speed for the motor has been acquired from aprevious iteration of the technique 100 for a particular bin. Accordingto the previous example, the new rated speed was estimated for a loadpercentage falling within Bin 1. Thus, if the present load percentagemeasured at block 104 again falls within Bin 1, a determination is madeat block 134 that the new rated speed for the motor has been acquiredfrom a previous iteration for that bin, indicated at 152, and thetechnique continues at block 150, where the new rated speed of the motoris used to recalculate the motor speed using the linear speed estimationalgorithm of Eqn. 1. If however, the present load percentage measured atblock 104 does not fall within Bin 1 (e.g., falls within Bin 2 or Bin3), then a determination is made at block 134 that the new rated speedfor the motor has not been acquired from a previous iteration for thatbin, indicated at 136, and technique 100 would perform blocks 138-146,as described above, for purposes of determining the new rated speed forthe motor for the particular bin within which the present loadpercentage measured at block 104 falls into.

Embodiments of the invention may be applied to motor assemblies thatinclude an AC motor fed by a fixed or variable frequency supply Also,the technique may be embodied in an internal module that receives asingle-phase current signal or in a stand-alone external moduleconfigured to receive any combination of single-phase, three-phase, ormulti-phase voltage and current signals. Further, while severalembodiments of the invention are described with respect to an AC motorand AC motor drive, it is contemplated that the technique set forthherein may be applied to a wide variety of applications, including fixedand variable voltage applications. Embodiments of the invention may relyon voltage, frequency, current, and/or power sensors of a motor driveand/or motor to determine input values for estimating motor speed. It isalso noted that embodiments of the invention allow for determination ofmotor speed at any arbitrary input voltage, any arbitrary inputfrequency, and any arbitrary load.

The above-described methods can be embodied in the form of computerprogram code containing instructions embodied in one or more tangiblecomputer readable storage media, such as floppy diskettes and othermagnetic storage media, CD ROMs and other optical storage media, flashmemory and other solid-state storage devices, hard drives, or any othercomputer-readable storage medium, wherein, when the computer programcode is loaded into and executed by a computer, the computer becomes anapparatus for practicing the disclosed method. The above-describedmethods can also be embodied in the form of a generically termed “speedestimation system” configured to estimate the speed of the rotor of theAC motor that would include a processor in the form of a speed detectionalgorithm unit and/or computer shown in the various embodiments of FIGS.1-5.

A technical contribution for the disclosed method and apparatus is thatit provides for a controller implemented technique for determining rotorspeed for fixed and variable supply frequency applications.

Therefore, according to one embodiment of the present invention, a rotorspeed estimation system is programmed to estimate a rotor speed of an ACinduction machine according to a linear speed estimation algorithm andbased on name plate information (NPI) of the AC induction machine andparameters of the AC induction machine during operation thereof, withthe parameters comprising voltage and frequency values of power input tothe AC induction machine and a load value of the AC induction machine.The rotor speed estimation system is also programmed to estimate a rotorspeed of the AC induction machine according to a frequency-domain signalprocessing algorithm and determine if the rotor speed estimated by thefrequency-domain signal processing algorithm is valid. If the rotorspeed estimated by the frequency-domain signal processing algorithm isvalid then the rotor speed estimation system estimates a tuned rotorspeed of the AC induction machine according to the linear speedestimation algorithm and based, in part, on the rotor speed estimated bythe frequency-domain signal processing algorithm and stores the tunedrotor speed on a computer readable storage medium.

According to another embodiment of the present invention, a method ofdetermining rotor speed of an AC induction machine includes accessingname plate information (NPI) of an AC induction machine, with the NPIincluding a rated power, a rated speed, a rated frequency, and a ratedvoltage of the AC induction machine. The method also includesdetermining each of a voltage value and a frequency value of power inputto the AC induction machine during operation thereof, determining a loadpercentage from the AC induction machine during operation thereof, andestimating a rotor speed of the AC induction machine in operation basedon the NPI, the voltage and frequency values of the AC inductionmachine, and the load percentage of the AC induction machine. The methodfurther includes calculating a revised rated speed of the AC inductionmachine, estimating a tuned rotor speed of the AC induction machinebased on the NPI, the voltage and frequency values of the AC inductionmachine, and the load percentage of the AC induction machine, with therevised rated speed replacing the rated speed from the NPI forestimation of the tuned rotor speed, and storing the tuned rotor speedon a computer readable storage medium.

According to yet another embodiment of the present invention, anon-transitory computer readable storage medium has stored thereon acomputer program comprising instructions which, when executed by atleast one processor, cause the at least one processor to acquire a firstestimate of a motor speed of an AC motor according to a linear speedestimation algorithm and based on name plate information (NPI) of the ACmotor and parameters of the AC motor during operation thereof. Theinstructions also cause the at least one processor to acquire a secondestimate of the motor speed of the AC motor according to afrequency-domain based speed estimation algorithm, perform a validationprocess on the second estimate of the motor speed of the AC motor, andcalculate a rated speed value for the AC motor based on the validatedsecond estimate of the motor speed of the AC motor. The instructionsfurther cause the at least one processor to input the calculated ratedspeed value into the linear speed estimation algorithm to acquire atuned estimate of the motor speed of the AC motor and store the tunedmotor speed on the computer readable storage medium.

The present invention has been described in terms of the preferredembodiment, and it is recognized that equivalents, alternatives, andmodifications, aside from those expressly stated, are possible andwithin the scope of the appending claims.

1. A rotor speed estimation system, the rotor speed estimation systemprogrammed to: estimate a rotor speed of an AC induction machineaccording to a linear speed estimation algorithm and based on name plateinformation (NPI) of the AC induction machine and parameters of the ACinduction machine during operation thereof, the parameters comprisingvoltage and frequency values of power input to the AC induction machineand a load value of the AC induction machine; estimate a rotor speed ofthe AC induction machine according to a frequency-domain signalprocessing algorithm; determine if the rotor speed estimated by thefrequency-domain signal processing algorithm is valid; and if the rotorspeed estimated by the frequency-domain signal processing algorithm isvalid, then: estimate a tuned rotor speed of the AC induction machineaccording to the linear speed estimation algorithm and based, in part,on the rotor speed estimated by the frequency-domain signal processingalgorithm; and store the tuned rotor speed on a computer readablestorage medium.
 2. The rotor speed estimation system of claim 1 whereinthe AC induction machine NPI comprises a rated power, a rated speed, arated frequency, and a rated voltage of the AC induction machine.
 3. Therotor speed estimation system of claim 2 further programmed to:calculate a revised rated speed of the AC induction machine based on therotor speed estimated by the frequency-domain signal processingalgorithm; and estimate the tuned rotor speed of the AC inductionmachine according to the linear speed estimation algorithm, wherein therevised rated speed of the rotor is input into the linear speedestimation algorithm in place of the rated speed from the AC inductionmachine NPI.
 4. The rotor speed estimation system of claim 3 furtherprogrammed to: characterize operation of the AC induction machine asfalling within one of a plurality of bins based on the load value; andcalculate a revised rated speed of the AC induction machine for each ofthe plurality of bins.
 5. The rotor speed estimation system of claim 2further programmed to: detect primary and secondary slot harmonics ofthe AC induction machine; and estimate a rotor bar number of the ACinduction machine based on one of the primary and secondary slotharmonics.
 6. The rotor speed estimation system of claim 5 furtherprogrammed to: acquire a pre-determined number of rotor bar numberestimates; identify a rotor bar number that repeats the greatest numberof times in the pre-determined number of rotor bar number estimates; andset the rotor bar number that repeats the greatest number of times asthe determined rotor bar number, R_(estimate).
 7. The rotor speedestimation system of claim 6 further programmed to: associate a rotorbar number of the AC induction machine with the rotor speed estimated bythe frequency-domain signal processing algorithm; compare the rotor barnumber from the frequency-domain signal processing algorithm with thedetermined rotor bar number, R_(estimate); and if the rotor bar numberfrom the frequency-domain signal processing algorithm is equal to thedetermined rotor bar number, R_(estimate), then determine that the rotorspeed estimated by the frequency-domain signal processing algorithm isvalid.
 8. The rotor speed estimation system of claim 1 furtherprogrammed to: forego tuning of the rotor speed estimated by the linearspeed estimation algorithm if the rotor speed estimated by thefrequency-domain signal processing algorithm is found to be invalid; andstore the untuned rotor speed estimated by the linear speed estimationalgorithm on the computer readable storage medium.
 9. The rotor speedestimation system of claim 1 wherein the AC induction machine comprisesan AC motor, and wherein the rotor speed estimation system comprises oneof a variable frequency drive, a motor protection device, a softstarter, and a removable device coupled to a motor drive of the ACmotor.
 10. A method of determining rotor speed of an AC inductionmachine, the method comprising: accessing name plate information (NPI)of an AC induction machine, wherein the NPI comprises a rated power, arated speed, a rated frequency, and a rated voltage of the AC inductionmachine; determining each of a voltage value and a frequency value ofpower input to the AC induction machine during operation thereof;determining a load percentage from the AC induction machine duringoperation thereof; estimating a rotor speed of the AC induction machinein operation based on the NPI, the voltage and frequency values of theAC induction machine, and the load percentage of the AC inductionmachine; calculating a revised rated speed of the AC induction machine;estimating a tuned rotor speed of the AC induction machine based on theNPI, the voltage and frequency values of the AC induction machine, andthe load percentage of the AC induction machine, with the revised ratedspeed replacing the rated speed from the NPI for estimation of the tunedrotor speed; and storing the tuned rotor speed on a computer readablestorage medium.
 11. The method of claim 10 further comprising: detectingslot harmonics of the AC induction machine; estimating a reference rotorbar number of the AC induction machine from the slot harmonics.
 12. Themethod of claim 11 wherein estimating the reference rotor bar number ofthe AC induction machine comprises: accessing a look-up tableassociating a number of poles of the AC induction machine, rotor barnumbers of the AC induction machine, and primary and secondary slotharmonics of the AC induction machine; and selecting the reference rotorbar number of the AC induction machine based on the look-up table. 13.The method of claim 11 further comprising: acquiring a pre-determinednumber of reference rotor bar number estimates; identifying a referencerotor bar number that repeats the greatest number of times in thepre-determined number of rotor bar number estimates; and setting thereference rotor bar number that repeats the greatest number of times asthe reference rotor bar number, R_(estimate).
 14. The method of claim 13further comprising: estimating a rotor slot speed and an associatedrotor bar number from the slot harmonics according to a frequency-domainsignal processing algorithm; comparing the rotor bar number associatedwith the rotor slot speed to the reference rotor bar number,R_(estimate); validating that the rotor bar number associated with therotor slot speed is equal to the determined rotor bar number,R_(estimate); and determining the revised rated speed of the ACinduction machine from the validated slot speed.
 15. The method of claim10 further comprising associating the revised rated speed of the ACinduction machine with one of a plurality of bins, each of the pluralityof bins defining a load percentage operating range of the AC inductionmachine.
 16. A non-transitory computer readable storage medium havingstored thereon a computer program comprising instructions which, whenexecuted by at least one processor, cause the at least one processor to:acquire a first estimate of a motor speed of an AC motor according to alinear speed estimation algorithm and based on name plate information(NPI) of the AC motor and parameters of the AC motor during operationthereof; acquire a second estimate of the motor speed of the AC motoraccording to a frequency-domain based speed estimation algorithm;perform a validation process on the second estimate of the motor speedof the AC motor; calculate a rated speed value for the AC motor based onthe validated second estimate of the motor speed of the AC motor; inputthe calculated rated speed value into the linear speed estimationalgorithm to acquire a tuned estimate of the motor speed of the ACmotor; and store the tuned motor speed on the computer readable storagemedium.
 17. The non-transitory computer readable storage medium of claim16 wherein the instructions further cause the at least one processor to:detect primary and secondary slot harmonics of the AC motor; andestimate a reference rotor bar number of the AC motor based on one ofthe primary and secondary slot harmonics.
 18. The non-transitorycomputer readable storage medium of claim 17 wherein the instructionsfurther cause the at least one processor to: acquire a pre-determinednumber of rotor bar number estimates; identify a rotor bar number thatrepeats the greatest number of times in the pre-determined number ofrotor bar number estimates; and set the rotor bar number that repeatsthe greatest number of times as the reference rotor bar number,R_(estimate).
 19. The non-transitory computer readable storage medium ofclaim 18 wherein the instructions further cause the at least oneprocessor to: associate a rotor bar number of the AC motor with thesecond estimate of the motor speed of the AC motor according to thefrequency-domain based speed estimation algorithm; compare the rotor barnumber determined from the frequency-domain based speed estimationalgorithm with the reference rotor bar number, R_(estimate); and if therotor bar number determined from the frequency-domain based speedestimation algorithm is equal to the reference rotor bar number,R_(estimate), then validate the second estimate of the motor speed ofthe AC motor.
 20. The non-transitory computer readable storage medium ofclaim 16 wherein the motor NPI comprises a rated power, a rated speed, arated frequency, and a rated voltage of the AC motor.